The present invention relates generally to a sheet cleaner for removing dust and debris from a substrate prior to printing on the substrate and more particularly to the conversion of a printing station into a cleaning station, in a multi-station printing apparatus.
In a screen printing process, ink is selectively applied to a surface or substrate. Dust or debris residing on the printing surface interferes with the application of the ink; areas of the surface under dust or debris will remain ink-free, yielding flaws in the resulting printed image. Dust and debris are generated particularly prolifically where substrates must be cut to size prior to the printing operation. Most particularly, dust and debris are created when a foam-core substrate is used and is cut prior to printing; this material yields dust which clings persistently to the printing surface due to static electricity. The problem of dusty substrates presents particular problems where volumes of printed sheets must be printed on relative quick turn-around. Stopping the printing apparatus to dust sheets by hand, or having to print extra sheets to replace flawed sheets, interferes with efficient printing.
A rotary screen printing apparatus provides a number of printing stations. At each printing station, one color of ink is applied. By passing the printing substrate through successive stations to receive ink of differing colors, multi-color printed matter is generated. For some print jobs, not all of the ink stations that are provided with the rotary screen printing apparatus are required. In such cases, one or more printing stations may be superfluous.
U.S. Pat. No. 6,158,343 describes the incorporation of a sheet cleaner in a rotary printing apparatus. This sheet cleaner is positioned adjacent to one of the printing stations. The sheet cleaner is a rolling cylindrical member. As a platen on which a sheet rests is rotated past the cleaner, the cleaner rolls across the printing surface in a direction generally perpendicular to the direction of movement of the ink applicator bar. This sheet cleaner does not take advantage of any of the precise mechanisms that control the path and pressure of the ink applicator bar. Further, this arrangement results in the cleaning of surface areas of the platen that extend beyond the sheet to be printed. This unnecessary cleaning causes the cleaning member to get unnecessarily dirty, requiring that it be cleaned or replaced relatively frequently.
The present invention provides a cleaning attachment for converting a printing station into a cleaning station. The invention further relates to a method for converting a printing station into a cleaning station by replacing either or both of the squeegee or flood bar with a cleaning attachment.
An object of the present invention is to use extra printing station capacity in a screen printing apparatus as a sheet cleaning station.
Another object of the present invention is to selectively convert a screen printing station into a sheet cleaning station with relatively minor modifications to the printing station.
Still another object of the present invention is to use existing printing mechanisms to manipulate the sheet cleaner to facilitate effective sheet cleaning.
Yet another object of the present invention is to use a tacky roller to collect dust and debris from a printing substrate.
Still another object of the present invention is to provide a sheet cleaning device which collects dust from the sheet to be printed without unnecessarily cleaning the surrounding platen surface.
Another object of the present invention is to provide a sheet cleaning device which is easily adjusted to use appropriate pressure to clean the sheet, regardless of the thickness of the sheet or substrate to be cleaned.
Still another object of the present invention is to provide a sheet cleaning device that operates simultaneously with printing being carried out at other printing stations, such that sheet cleaning does not delay printing operations.
Yet another object of the present invention is to provide a retrofit cleaning assembly for use on a rotary screen printing apparatus.
Another object of the present invention is to provide a cleaning assembly that allows for convenient cleaning of the cleaner.
Still another object of the present invention is to provide a cleaning assembly that can easily replace printing tools on a screen printing apparatus to convert a printing station into a cleaning station, and for the conversion to be easily reversible, such that when necessary for a given print job, all print stations can be employed for printing, but when not necessary, one station can be used for cleaning.
Another object of the present invention is to provide a simple, easy-to-use, low-cost, flexible and speedy apparatus and method to clean a sheet prior to printing.